Background: CT scans are frequently done after minor head injury to evaluate for intracranial hemorrhage. While CT scans are an excellent tool for diagnosing or ruling out this disorder, they are not without harms including radiation exposure, cost and department delays. Much of the time, CTs are negative, or find injuries for which no intervention is ever done and do not clinically affect the patient. Clinical Decision Instruments may aid clinicians in determining which patients are higher risk and require imaging and which do not.

For the purpose of this blog post, minor head injury was defined as witnessed Loss of Consciousness (LOC), definite amnesia, or witnessed disorientation in a patient with a GCS of 13-15.

Clinical Question: Can a clinical decision instrument safely determine which patients with minor head injury do not need advanced imaging?

To answer this question, we are going to review two articles:

Stiell I et al. The Canadian CT Head Rule for patients with minor head injury. Lancet. 2001 PMID: 11356436

Let’s take the Canadian CT Head “Rule” first

Population: Adult patients presenting to the emergency departments at 10 large Canadian hospitals with Glascow Coma Scale 13 or greater within 24 hours after blunt head trauma resulting in witnessed loss of consciousness, amnesia, or witnessed disorientation.

Intervention: Standardized clinical assessments were performed on all consecutive eligible patients before performing a CT scan at the discretion of the attending physician.

Comparison: They took all the pre-CT variables and compared them with the CT and outcomes at 14 days looking for associations. From there they selected the combination of variables that would give the highest sensitivity/specificity for detecting the outcome measures using logistic regression and recursive partitioning. Overall, 44 variables were assessed (24 primary and 20 created by cut-offs/combinations)

Outcome (Primary): Need for neurological intervention, defined as death within 7 days due to the head injury or need within 7 days for craniotomy, elevation of skull fracture, intracranial pressure monitoring, or intubation for head injury

Outcome (Secondary): Clinically important brain injury on CT, defined as any acute brain finding on CT that would normally require admission to a hospital and neurological follow-up. 94 patients (4%) were judged to have clinically unimportant lesions on CT.

Design: Multicenter, prospective, cohort study.

Excluded:

Age under 16

Minimal head injury with no LOC, amnesia, or disorientation

Unclear history of trauma as the primary event (ie primary seizure or syncope)

Obvious penetrating skull injury or depressed fracture

Acute focal neurological deficit

Unstable vital signs associated with major trauma

Seizure prior to ED assessment

Anticoagulation or bleeding disorder

Pregnancy

Clinical Bottom Line

3121 patients were enrolled and assessed for the primary outcome measure, need for neurological intervention.

Initial GCS was 15 in 80% of patients.

2078 were scanned (67%) meaning 1043 were not scanned (33%)

A decision tool was created including 7 variables formed through logistic regression followed by recursive partitioning.

Secondary Outcome: Sensitivity and specificity of the overall rule (all 7 variables) were 98.4% and 49.6%.

There were 254 patients (8%) were judged to have a clinically important brain injury.

The tool identified 250 of the 254 cases.

The four patients not identified with the tool were small contusions. None required neurosurgical treatment and none had neurological sequelae.

Strengths:

Large, multicenter trial

Study asked a clear clinical question that was patient centered

Outcome measures were objective reducing bias

Limitations:

33% of patients in the study did not have CT performed

Although phone follow up was complete on those patients not getting CT in the ED, follow up only went out to 14 days

Authors Conclusions:“We have developed the Canadian CT Head Rule, a highly sensitive decision rule for use of CT. This rule has the potential to significantly standardise and improve the emergency management of patients with minor head injury.”

Now, let’s tackle the New Orleans “Rule”

Population: Adult patients > 18 years of age with blunt head trauma within 24 hours of presentation who had LOC, amnesia or disorientation but presented with a GCS = 15. All patients had normal neurologic examinations.

A decision tool was created including 7 variables formed through logistic regression followed by recursive partitioning.

Headache

Vomiting

Age over 60

Crug or alcohol intoxication

Deficits in short-term memory

Physical evidence of trauma above the clavicles

Seizure

Critical Findings

Sensitivity 100%

57 patients with positive CT scan

All caught by clinical decision instrument

Specificity 25%

Strengths:

All patients in the study had CT scan performed on initial evaluation

No patient with an intracranial injury was missed by the clinical decision instrument

Limitations:

Specificity is very low (25%) which means many patients will be positive by the instrument but won’t have findings on head CT

Unlike the Canadian rule, this rule was looking for ANY intracranial injury, not necessarily ones that are clinically significant

Authors Conclusions:“For the evaluation of patients with minor head injury, the use of CT can be safely limited to those who have certain clinical findings.”

Our Conclusions: The Canadian Head CT instrument was a high-quality study with a good sample size. The final decision instrument had excellent sensitivity for detecting clinically relevant intracranial injuries (defined here as requiring neurosurgical intervention) but even the expanded rule will miss a small portion of patients with identifiable intracranial injuries (although not clinically significant ones).

The New Orleans study derived and prospectively validated a clinical decision instrument with a very high sensitivity and very poor specificity. Unlike the Canadian Head CT instrument, it identifies ALL intracranial injuries regardless of whether they are clinically significant or not. The low specificity limits the utility of this instrument.

Subsequent studies have compared the New Orleans and Canadian head CT decision instruments (Papa 2012, Smits 2005) and found that both rules perform with 100% sensitivity for finding injuries that require neurosurgical intervention. The New Orleans criteria perform better for finding all injuries but, as a result, has a much lower specificity. Smits et al estimated that adoption of the New Orleans rule would result in a modest 3% reduction in CT utilization while adoption of the Canadian head CT instrument would result in a 37.3% reduction (Smits 2005).

Potential to Impact Current Practice: These decision instruments continue to be widely used today by clinicians to help guide decision-making in minor head injuries. These articles were both named on the ALiEM’s Landmark Articles list.

Bottom Line: The New Orleans head CT criteria allow clinicians to identify all patients who will have intracranial injuries whether they are clinically significant or not but is unlikely to produce anything more than very small reductions in CT utilization. The Canadian Head CT decision instrument is a highly sensitive tool for determining which patients with minor head injury do not need emergent advanced imaging performed.